Efficient lead-free flotation separation of malachite from calcite and quartz by using amidoxime collectors

3-Ethyl-4-pyridylamidoxime (EPA) and 3-methyl-5- tert -butyl-4-pyridylamidoxime (MBPA) were introduced as the collectors in the flotation and enrichment of malachite from calcite and quartz. Compared with MBPA and the traditional collector benzohydroxamic acid (BHA), EPA exhibited a better flotation performance. Its collecting ability to malachite was stronger than BHA, and its selectivity toward calcite and quartz was better than MBPA. In the absence of Pb 2 + ions, 2.0 × 10 −4 mol/L EPA at pH 8.0 could recover about 86 % malachite, 20 % calcite and 22 % quartz. Under the same conditions, BHA floated out around 58 % malachite, 27 % calcite and 10 % quartz. The contact angle and SEM proved that EPA could enhance the surface hydrophobicity of malachite via corrosion to produce more active sites for its heavy adsorption. FTIR and XPS revealed that EPA would chelate with the surface Cu atom to form -O-Cu and -N-Cu bonds. EPA owned stronger electron-donating ability and worse electron-accepting ability than BHA, which brought a stronger chemical reactivity. Moreover, its isomer could further enhance the adsorption ability onto malachite. The novel amidoxime collector EPA was able to efficiently lead-free enrich malachite and enhance the industrial capacity to treat copper oxide ores.